1. Field of the Invention
The present invention relates generally to a tensioner guide used in a chain drive unit for applying a tension to a transmission chain to prevent the transmission chain from whipping or becoming slack while running, and more particularly to a tensioner guide suitable for use in an application where the tension side and slack side of a transmission chain are reversed or switched over during operation of the chain drive unit.
2. Description of the Related Art
In a chain drive unit having two sprockets disposed in spaced relation to form a drive side and a driven side of the chain drive unit, when the direction of rotation of the sprocket on the drive side is reversed or when the drive side and driven side of the chain drive unit are reversed, a tension run and a slack run of the transmission chain that are provided on opposite sides of the drive sprocket are reversed in position.
To deal with this problem, the chain drive unit may include, as shown here in FIG. 4, two stationary guides 30, 31 provided outside a loop of the transmission chain 32, with shoe surfaces 30a, 31a of the respective guides 30, 31 being in sliding contact with a tension run and a slack run of the transmission chain 32 to guide running of the transmission chain 32 over two spaced sprockets 33, 34.
The stationary guides 30, 31 provided on both of the tension and slack sides of the transmission chain 32 have a problem that when the chain 32 undergoes elongation due to a long period of use, vibration of the chain 32 while running is amplified and eventually causes the slack run of the chain 32 to beat or whip the shoe surface 31a of the confronting stationary guide 31. This operation generates unpleasant operation noises and accelerates wearing out of the shoe surface 31a.
Another conventional chain drive unit shown in FIG. 5 includes a stationary guide 35 disposed on one side of a transmission chain 36 trained over two sprockets 37, 38, with a shoe surface 35a being in sliding contact with a free run of the chain 36, and a pivotable guide 39 disposed on the other side of the chain 36 and pivotally supported on a fixed mounting shaft 40 with a shoe surface 39a being pressed against and in sliding contact with a free run of the chain 36 by means of a tensioner 41 acting on an oscillating free end of the pivotable guide 37 from the back side of the free end. With this arrangement, whenever the free run of the chain 36 which is in sliding contact with the stationary guide 35 forms a tension run of the chain 36, an elongation of the chain 36 caused due to aging, for example, can be taken up by pivotal movement of the pivotable guide 39 caused by the action of the tensioner 41. Thus, the chain 36 while running does not cause oscillation and slackening of the slack run.
However, when the chain free run being in sliding contact with the stationary guide 35 is arranged to form a slack run, the pivotable guide 39 is urged backwardly by a free run of the chain 36 being stretched or tensioned, and slack in the chain slack run is increased. The chain slack run with increased slack tends to beat the shoe surface 35a of the stationary guide 35, generating unpleasant operation noises and accelerating wearing-out of the shoe surface 35a, in the same manner as the prior art shown in FIG. 4.